The disposal of old or reclaimed newsprint has become a serious ecological problem. Currently the United States uses approximately 13,000,000 tons of newsprint annually and yet only about 3,000,000 tons are recycled. The major portion of old newsprint is deinked and used in newsprint production, while a minor portion is used in certain paperboard products, such as folding carton grades, which have low strength requirements. The recycling of old newsprint has been limited due to its low tear strength. Virgin newsprint stock is normally produced from ground wood and contains relatively short fibers, and has a low tear strength. The pulping of old newsprint further reduces the fiber length, so that the amount of old newsprint pulp that can be used in combination with virgin newsprint pulp is limited.
Newsprint is an extremely difficult grade of paper to produce, due to its low tear strength, and to be made competitively it is produced at very high speeds with machines running in excess of 4500 fpm. For this reason, the level of cleaning required is very great to produce a commercially acceptable product using old newsprint as a fiber supply.
When using old newsprint as a fiber supply in the production of newsprint, the old newsprint, after pulping, is deinked by one of a number of conventional deinking processes, such as described in "Beloit Corporation Deinking Manual", 2nd Ed., 1979. In general, the deinking process acts to remove ink from the fibers with minimum fiber damage and to disperse the ink particles freely in the aqueous pulp suspension to enable subsequent mechanical separation or removal. In the typical deinking process the old newsprint is pulped with water and chemical dispersants and the shear forces encountered during the pulping provide some mechanical dispersion of the ink. In addition, the dispersants act to chemically disocciate the ink from the fibers.
Once the ink has been chemically separated from the fibers, there are two basic manners for the removal of the ink from the pulp slurry. One is dilution washing which is a mechical process of rinsing the ink particles from the pulp, while the second is froth flotation, which is a chemical/mechanical process of selectively floating the ink particles from a dilute pulp suspension.
After deinking, the deinked old newsprint pulp can then be used in combination with virgin newsprint pulp in the production of newsprint.
Corrugated paperboard consists of a central layer of corrugated medium sandwiched between two outer layers of linerboard. Linerboard typically is a two-ply product having a basic weight of 20 to 90 lbs. per 1,000 sq. ft. The base ply can be composed of Kraft pulp or recycled or old corrugated containers, while the top or outer ply normally consists of virgin Kraft pulp to cover up the visual containments in the base ply. In some situations, the outer or top ply may be composed of bleached fibers to improve the visual appeal of the corrugated product.
Approximately 20,000,000 tons of linerboard are produced annually in the United States. It is apparent that if old newsprint could be incorporated as a component of linerboard, it would provide a substantial use for the old newsprint which is presently being discarded. However, because of the short fiber characteristics of old newsprint and the presence of substantial fines, old newsprint has been considered totally unacceptable for use in a paperboard product having high strength requirments, such as linerboard.